The present invention relates generally to digital data communication systems. More particularly, the present invention relates to a new and improved method and apparatus for providing power to a communication device over communication wires coupled to the device.
Communication systems have become increasingly important for individuals and businesses in the modem world. Because reliable communication systems are integral to most businesses, a loss of power to a business"" communication system can have severe consequences for the business and its customers. For example, equipment such as an automated teller machine may become entirely useless upon a loss of power to its communication system. Because of undesirable financial and other consequences, many telecommunication systems utilize xe2x80x9calways onxe2x80x9d data and voice services. Thus, the increasing importance of communications has created a need for reliable backup power sources.
Prior art systems have used a number of methods to provide backup power to communication devices. For example, some businesses use generators to supply backup power to help keep essential services operational. However, these generator systems tend to be expensive and their use is typically limited to larger facilities. Batteries are also widely used to provide such a backup supply of power. Unfortunately, the use of batteries to supply backup power is deficient in a number of respects. First, batteries can only supply backup power for a limited amount of time. Thus, long power outages may exhaust the reserve supply of power stored in the batteries. Furthermore, batteries have a limited shelf life and, if not checked frequently and replaced, may have expired prior to the power outage. In addition, batteries may contain chemicals that pose environmental hazards and, thus, require specialized and expensive disposal.
Span power is used to power some communication devices such as a telephone providing plain old telephone service (POTS). Span power is supplied to the communication equipment on communication wires that are separate and distinct from the wires of the local electrical utility. This is the reason that a standard telephone will usually work even when power form the local utility is unavailable. Span power for POTS is a relatively economical and reliable backup power supply when compared to batteries. The voltage values associated with conventional communication equipment are low enough that they are generally not considered to be hazardous to people that may make contact with the voltages. Nevertheless, the central office communications equipment adapted to furnish a DC power signal as part of a data signal typically utilizes ground fault interruption (GFI) circuitry and current limiting devices for the protection of craftsmen and customers. However, due to the voltage and current limitations, the span power supplied over traditional telephone lines is only capable of providing a very limited amount of power, typically on the order of 50 milliwatts. This amount of power is insufficient to power many modem telecommunication devices. Providing a sufficient amount of span power to modern communication devices requires special wiring and restricted consumer access to the power supply in order to adhere to safety standards and building codes. Thus, traditional span power has some severe limitations, and if modified to provide sufficient power to modem communication devices, a substantial amount of expense may be incurred.
Therefore, what is needed is an economical and reliable method and apparatus for supplying power to a communication system when the local power supply is not available. The method and apparatus should be capable of supplying sufficient power for modem telecommunications equipment. Furthermore, the method and apparatus should conform to relevant safety standards and building codes in order to minimize the chance of harm to users of the communications equipment.
The preferred embodiment of the present invention is directed toward a method of delivering power to a customer premise over a twisted pair of wires used as a communication media for sending communication signals between a central location and the customer premise. The method combines a high voltage direct current (HVDC) signal with the communication signal to produce a combined signal at the central location. The combined signal is sent from the central location to the customer premise over the twisted pair. The HVDC signal is separated from the combined signal proximate the customer premise to provide a customer premise HVDC signal. The customer premise HVDC signal is then converted to a customer premise low voltage direct current (LVDC) signal. Most preferably, the converting of the customer premise HVDC signal to the customer premise LVDC signal is performed at a restricted location proximate the customer premise such that customer access to the customer premise HVDC signal is minimized. In an especially preferred embodiment, the HVDC signal has a value in the range of approximately 100-250 volts and the LVDC signal has a value in the range of approximately 25-75 volts. The customer premise LVDC signal is coupled to interior telecommunication wiring in the customer premise.
The above discussed embodiment provides a reliable power supply that is independent of a local power supply circuit. The HVDC power signal provides sufficient power for communication equipment while limiting the current to the capacity of the twisted pair. In addition, converting the HVDC power signal into a LVDC power signal at the customer premise produces a voltage that is less likely to injure persons that may come into contact with the communication system. Thus, the preferred embodiment of the present invention solves many of the aforementioned deficiencies of the prior art power supplies.
The present invention further provides a new and improved system for providing power from a central location to a remote location wherein communication signals are transferred between the central location and the remote location on communication wires. The system includes a high voltage power supply located at the central location. The high voltage power supply provides a HVDC power signal that is coupled to the communication wires. A voltage conversion unit located at the remote location is also coupled to the communication wires. The voltage conversion unit is preferably placed in a restricted area at the remote location such that human access to the HVDC power signal is minimized. The voltage conversion unit receives the HVDC power signal and converts the HVDC power signal to a LVDC power signal. The LVDC power signal is then coupled to premise communication wires located at the remote location. In order to maintain a good signal to noise ratio (SNR), filtering is used to limit the amount of noise produced by the voltage conversion unit that couples into the premise communication wires.
In an alternative embodiment, the voltage conversion unit includes a communication transformer having a first primary winding, a second primary winding, a first secondary winding, and a second secondary winding wherein each of the windings has first and second ends. The first ends of the first and second primary windings are electrically connected to the communication wires. An HVDC-to-LVDC converter (converter) has an input connected to the second ends of the first and second primary windings and has an output connected to the first ends of the first and second secondary windings. The second ends of the first and second secondary windings are electrically connected to the remote wires. The converter is configured for receiving HVDC power from the communication wires through the primary windings and applying LVDC power to the remote wires through the secondary windings. The communication transformer provides a path for communication signals to pass to and from the communication wires and the premise communication wires.
The above described system improves upon the prior art by providing a reliable power supply that avoids the replacement issues associated with using batteries as a source of power. Furthermore, by converting the HVDC power signal to a LVDC power signal, the above described system allows a sufficient amount of power to be transmitted to a remote location while minimizing contact at the remote location to hazardous voltage levels. Thus, the above described system substantially improves upon the prior art.